Single core series-shunt ferroresonant voltage regulator with easily altered gap



May 27, 1969 T H. P. HART 3,447,068

I SINGLE CORE SERIES-SHUNT F E I ERRORESONANT VOLTAG REGULATOR WITH EASILY- ALTERED GAP Filed Dec. 20, 1966 FIG.

ATTORNEY I U.S. Cl. 32360 United States Patent 0 3,447,068 SINGLE CORE SERIES-SHUNT FERRORESONANT VOLTAGE REGULATOR WITH EASILY ALTERED GAP Harry P. Hart, Whippany, NJ., assignor to Bell :Ielephone Laboratories, Incorporated, Berkeley Heights, NJ., a corporation of New York Filed Dec. 20, 1966, Ser. No. 603,245 Int. Cl. H02p 13/04; H02j 3/12 6 Claims ABSTRACT OF THE DISCLOSURE The connecting bar at one end of a three-legged magnetic core is spaced a uniform distance from the-legs to form an easily altered gap, and a magnetic shunt joins the three legs at a point between the end bars. The linear inductance is wound on the center core leg between the shunt and the gap, and the saturating inductor, which is shunted by the ferrocapacitor, is wound on the center leg separated from the linear inductor by the shunt. The linear and saturating inductors, serially connected across the source in opposite polarity, develop aiding magnetomo.ive forces to effect ferroresonant regulation.

This invention relates to power transformation apparatus and more particularly to a ferroresonant voltage regulator.

Many alternating current voltage regulating systems have exploited the properties of magnetic devices as, for example, the arrangements which include nonlinear indoctors in tuned circuits. These circuits are known getterally as ferroresonant regulators and employ saturable cores for the nonlinear inductance. While numerous ferroresonant regulator circuit designs exist, they may generally be categorized into shunt and series-shunt configurations. Each of these configurations comprises a nonlinear inductance, a linear inductance, and capacitor combined in a tuned circuit arrangement to provide an AC output voltage which has a relatively constant volt-second area despite variations of AC input voltage.

One typical design is the shunt configuration where a single winding is connected directly across the line. This configuration is typified by US. Patent 2,143,745 granted to J. G. Sola wherein all the coils are wound on a single core constructed with a magnetic shunt which includes an air gap. By virtue of the shunt magnetic circuit the equivalent circuit presented to the load includes a linear inductance characteristic. With increased development of the shunt type configuration it has been found that a superior regulating characteristic may be obtained at reduced cost by departing from the nonstandard laminations used in the Sola patent and constructing the core from standard size interwoven E and l laminations on which a separate magnetic shunt is placed to provide the required leakage path. However, in applications requiring the ferroresonant regulator to feed a capacitive input filter, it has been foundthat the air gap in the magnetic shunt must be'critically adjusted if optimum performance over a wide load range is to be obtained.

In the series-shunt ferroresonant regulator configuration the linear and nonlinear inductors are individual coils serially connected across the line. As in the shunt type regulator, a capacitor connected across the nonlinear inductor is tuned to insure saturation of the nonlinear inductor at the frequency and voltage of the line source. Unlike the shunt type regulator configuration. however, the linear and nonlinear inductances of the existing seriesshunt regulators are wound on separate cores and therefore present a greater physical bulk than the shunt type.

'this configuration.

Accordingly, it is an object of this invention to provide an improved ferroresonant AC voltage regulator.

It is another object of this invention to provide a seriesshunt type ferroresonant regulator wound on a simply constructed single core.

In accordance with the objects of the present invention a series-shunt type ferroresonant regulator is constructed with. a single core fashioned from laminations of magnetic material. A two-window core is formed by placing a stack of E-sltaped laminations next to a separate stack of I-shaped laminations. The stacks are positioned so that the lshaped stack perpendicularly adjoins the three horizontal bars of the E-shaped group with a nonmagnetic gap as the interface between the stacks. Two

stacks of laminations of magnetic material are placed into the windows encompassed by the three horizontal bars of the E-shaped stack to form a shunt in the magnetic circuit of the core. A linear inductance is constructed by winding a coil about the middle of the three bars on the E-shapcd laminations on the side of the magnetic shunt which is nearest to the stack of I-shaped laminations. A nonlinear inductance coil and output winding are also wound about the middle bar but on the other side of the magnetic shunt. The linear and nonlinear inductances are serially connected with opposing polarities across the AC input source, and a capacitor connected across the nonlinear inductance coil is tuned so that it insures saturation of the core portion of the nonlinear inductor at the frequency and voltage of the source. By virtue of this construction a series-shunt ferroresonant regulator of reduced bulk and cost can be obtained with a single core which does not require interweaving of core laminations.

These and other objects and features of the invention will be better understood upon consideration of the following detailed description when taken in connection with the accompanying drawing in which:

FIG. 1 is a detail view of the construction of an embodiment of the invention; and

FIG. 2 is a schematic representation of the electrical circuit of the embodiment of FIG. 1.

The regulator as shown in FIG. 1 includes three coils wound on a magnetic circuit constructed from magnetic material having a suitable hysteresis loop. The core is formed by placing a stack of I-shaped laminations 4 in close proximity to a stack of E-shaped laminations 5with a nonmagnetic spacer 7 at the interface. The components are then joined so that the I laminations are perpendicular to the three bars of the E laminations. A suitable magnetic shunt 6 is tightly fitted into the windows of the stack of E-shaped laminations to form a low reluctance path between the middle bar and the adjacent outer bars. The nonmagnetic spacers 7 provide a high reluctance path necessary for the operation of the regulator.

As an aid in the explanation of the circuit operation, the middle of the three bars on the stack of E-shaped laminations is divided graphically into two regions-an upper region A separated from a lower region B by the magnetic shunt 6. Coil l is wound over region A of the coil while coils 2 and 3 are wound over region B so that the magnetic shunt 6 separates coil 1 from coils 2 and 3. One end of coil 1 is connected to a first terminal of an unregulated AC source 8, while the other end of coil 1 is connected to an end of coil 2. A second terminal of source 8 is connected to a tap point on coil 2 and a capacitor 9 is connected across the full length of coil 2. Coil is an output winding which is connected through a rectifier and filter 10 to the load. The capacitor size is chosen and coils l and 2 are interconnected so that, at the frequency and voltage of source 8, the current in coil 2 will establish a magnetomotive force and flux in core portion B in a direction which is aiding to the flux present in the portion A due to the current in winding 1. The specific interconnections amongst coils 1 and 2 and source 8 have an important bearing on the regulation of the device as will be further explained hereinafter. Shunt 6, it may be noted, forms part of the magnetic circuit of each of the coils 1 and 2.

FIG. 2 is a schematic diagram of the electrical circuit of the structure shown in FIG. 1 and is generally representative of the series-shunt type ferroresonant regulator circuits. As can be seen from FIG. 2, the circuit includes a linear inductor 1, a nonlinear inductor 2 and a capacitor 9 tuned as described heretofore. The linear inductance is fashioned by winding coil 1 on the high reluctance magnetic circuit path which includes nonmagnetic gap 7. The main flux path for this circuit includes portion A of the center bar of the stack of E laminations, gap 7 at the center bar and a pair of parallel return paths. Each of the return paths includes a portion of the stack of I laminations, gap 7 at the outer bars an outer bar of the stack of E laminations and the magnetic shunt 6. Gap 7 in this magnetic circuit path is preadjusted to insure that no portion of the iron will saturate at the voltages of the source when the number of turns of coil 1 is appropriately limited.

The nonlinear inductance is fashioned by winding coil 2 with a sufficient number of turns about the core portion B and selecting the value of capacitor 9 as described heretofore. The main flux path for the saturating portion of the core includes core portion B of the middle bar of the stack of E-shaped laminations, the magnetic shunt 6 and a return path which includes each of the end bars and the connecting bar of the E-shaped stack of laminations. In accordance with techniques well known in the art, saturation of the magnetic circuit portion which includes coil 2 can be obtained by properly designing the number of turns for coil 2, the area (i.e., number of laminations) of theliux path, and the value of capacitance 9.

The load handling capacity of a ferroresonant regulator is known to be proportional to CB where C is the capacitance of capacitor 9 and E the voltage across it. Consequently, the capacitance and voltage capabilities of capacitor 9 must be large enough for the frequency and voltage of source 8 to ensure saturation of the core portion at the intended loads. The size of capacitor 9 can, however, be somewhat reduced by connecting capacitor 9 across a greater number of turns on coil 2 while simultaneously keeping CE fixed.

The core is constructed so that there is flux leakage between the magnetic circuit paths of the linear and nonlinear coils. By connecting the coils as described, the flux from core portion A (i.e., the linear magnetic circuit path) aids the flux in the portion B (i.e., the saturating magnetic circuit path to aid in saturating core portion B and hereby to obtain a more effective regulation. Furthermore, the magnetic coupling of the linear and nonlinear inductances also provides a degree of load compounding. With the output coil 3 tightly coupled to the nonlinear coil 2, any change in load current is manifested as a corresponding change in the current in winding 2 so that the total current drawn from the source and the current in winding 1 increases with load. Therefore, the flux swing in portion A of the core increases with load and the flux leakage into portion B of the core aids to provide the desired load compounding.

A more detailed theoretical explanation of the operation of the series-shunt type ferroresonant regulator may be found in Nonlinear Magnetic Control Devices" by r W. A. Gcyger, published 1964. A brief explanation of the basic mechanism by which voltage regulation is obtained in such a l'errorcsonunt regulator design may be had by considering the time integral of voltage across winding 3 or across the nonlinear inductor which includes coil 2.

The definite time integral of voltage across winding 2 must reach a certain value in order to swing the flux in the saturating portion B of the core from one saturation level to another. Since only one such flux swing can occur for each half cycle of the input voltage from source 8, the half cycle average voltage across winding 2 or 3 is equal to the above-mentioned definite time integral of voltage across winding 2 divided by the half period of the input voltage. Thus by virtue of the saturating properties of the core the half cycle average voltage across the winding 2 or 3 is held constant.

In the prior art, the cooperation of capacitor 9 with saturating inductance 2 has been explained in various ways. The most satisfactory explanation appears to be that the capacitor 9 provides peak-to-peak regulation as well as root mean square regulation of the voltage across winding 2 or 3. Since saturating the core of nonlinear inductance 2 merely holds constant the half cycle average value of the voltage, the voltage peaks may simultaneously be very tall and very narrow or very short and very wide without disturbing the half cycle average value. The introduction of capacitor 9 produces an improved proportioning between the height of a voltage peak and its width at any given point below that peak as capacitor 9 charges and discharges in response to voltage changes across winding 2. This proportioning effect combined with half cycle average voltage regulation results in peak-to-peak voltage regulation as well as root mean square voltage regulation.

The output winding 3 is tightly coupled to winding 2 so that its induced voltage is proportional to the voltage across the nonlinear inductance 2. The output coil 3 is shown with a center tapped connection to a full wave rectifier and a capacitor filter. The rectifier and filter circuit are illustratively shown and may, in accordance with this invention, bechanged to suit any other application. it is noted, however, that the value of capacitor 9 is only one half the value required for resistive load and choke input filter because of the reflected benefit of the filter capacitor 11.

By virtue of the core construction described, the nonmagnetic gap 7, provided to obtain the linear inductance, may be adjusted during the manufacturing process; The thickness of the gap can easily be adjusted by simply using the desired thickness of nonmagnetic spacer material and adjusting that thickness as needed. In this connection, it is known that the adjustment of the gap in applications where a ferroresonant transformer feeds a capacitor input filter is critical in order to obtain optimum performance over a wide load range. While other ferroresonant regulator arrangements might require the costly shaving of magnetic material in order to obtain the proper gap, the instant arrangement simply requires the insertion of the proper thickness spacer. This of course is a source of significant savings in construction cost. Additionally, the fabrication of a core from a stack of laminations which are not interwoven is a further saving in manufacturing cost.

It is therefore to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements ma be devised by those skilled in the art Without departing from the spirit and scope of the invention.

What is claimed is:

1. A voltage regulating circuit comprising a single core of magnetic material, a linear inductor including a first magnetic circuit portion of said core and a first coil coupled to said first portion, a saturating inductor including a second magnetic circuit portion of said core and a second coil coupled to said second portion, an AC source. means for serially connecting said linear and saturating inductors in opposite polarity to said AC source, a capacitor connected across said saturating inductor having a value sullicicnt to cause saturation in said second magnetic circuit portion of said core.

2. A voltage regulating circuit in accordance with claim 1 wherein said oo-re includes a group of stacked E shaped laminations, a group of stacked I laminations adjacent to the three bars of said stacked E-shaped laminations to form a pair of windows, and a magnetic shunt fitted into the windows to provide a low reluctance path between the intermediate bar and the outer two of said three E bars.

3. A voltage regulating circuit in accordance with claim 2 wherein said first magnetic circuit portion includes a nonmagnetic spacer fiorming a gap between said stack of I laminations and said stack of E laminations and said magnetic shunt includes a pair of stacked laminations of magnetic material positioned between the intermediate one and the outer ones of the three bars of said stack of E shaped laminations.

4. A voltage regulating circuit comprising a single magnetic core which includes a stack of E-shaped magnetic laminations, a nonmagnetic spacer adjacent to the three bars of said stack of E-shaped larninations, a stack of I-shaped magnetic Iarninations separated from said stack of :E-shaped laminations by said spacer, and a low reluctance magnetic shunt including a pair of stacked latminations individually positioned between the intermediate one and outer two of said three E bars, a linear inductor including a first coil wound on a first portion of said intermediate bar between said shunt and said spacer, a saturating inductor including a second coil wound on a second portion of said intermediate bar separated from said first coil by said shunt, an output coil wound on said second portion of said intermediate bar, an AC source, means for serially connecting said linear and saturating inductors in opposite polarity to said AC source, and a capacitor connected across said saturating inductor having a value sufiicient to cause saturation in said second portion of said intermediate bar.

5. A voltage regulating circuit in accordance with claim 4 wherein said first and second coils are connected to produce additive magnetomotive forces.

6. A voltage regulating circuit in accordance with claim 5 wherein said AC source is connected to a tap point of said second coil.

References Cited UNITED STATES PATENTS 2,143,745 1/1939 Sola 323-60 2,268,212 12/1941 Holubow 323-61 2,634,392 4/ 1953 Pohm.

3,219,916 11/1965 Hart. 3,286,159 11/1966 Kuba 323-81 X 3,341,766 9/1967 Rhyne 323-60 X 3,371,263 2/1968 Walz et al. 321

JOHN F. COUCH, Primary Examiner. G. GOLDBERG, Assistant Examiner.

U.S. Cl. X.R. 323-81; 336--214 

